U.S. officials have identified four Las Vegas casino workers among 300 Bosnian immigrants who they believe concealed their involvement in wartime atrocities, including the 1995 Srebrenica massacre, and are trying to deport at least 150 of them, The New York Times reported Saturday.

The immigrants were among refugees fleeing the violence in Bosnia after a war that erupted in 1992 with the collapse of Yugoslavia. The number of suspects eventually could exceed 600 as more records from Bosnia become available, the newspaper reported.

“The more we dig, the more documents we find,” Immigration and Customs Enforcement historian Michael MacQueen, who has led many of the agency’s war crimes investigations, told the Times.

Many of the Bosnian suspects were soldiers, and they include a Virginia soccer coach, an Ohio metal worker and four Las Vegas hotel-casino workers, the newspaper said. The four Las Vegas residents were not further identified by the newspaper. Some are now U.S. citizens, it said.

A spokeswoman for U.S Immigration and Customs Enforcement reached by the Review-Journal on Saturday said privacy laws prevent her from identifying the four men unless they are charged with a crime. She said she did not know their current status. The men’s Arizona-based attorney, Christopher Brelje, could not be reached for comment Saturday.

The Times said evidence indicates half of the 300 Bosnian suspects might have played a part in the massacre at Srebrenica, where 8,000 Muslim men and boys were killed by Bosnian Serb forces in five summer days in 1995, toward the end of a war that claimed 100,000 lives.

The massacre was the culmination of a policy of ethnic cleansing by Bosnian Serb military commander Ratko Mladic’s forces to carve a pure Serb state out of diverse Bosnia.

Lawyer Thomas Hoidal represented two of 12 Bosnian Serbs in Arizona who face deportation over war crimes.

“It’s guilt by association,” he told the Times.

The Bosnian war ended in a 1995 U.S.-brokered peace deal. A U.N. tribunal subsequently ruled that genocide was committed in Bosnia.

This was not the first time a Las Vegas resident has been implicated in the Srebrenica massacre.

Identified as a former Bosnian-Serb police commander, Dejan Radojkovic, 64, of Las Vegas, entered the United States in 1999 and was arrested by federal law enforcement in 2009. ICE later announced that an immigration judge had ordered Radojkovic deported on grounds that he either ordered or directly participated in the massacre. Radojkovic was deported to Bosnia and Herzegovina in May 2012, according to ICE.

For years, ICE’s Human Rights Violators and War Crimes Unit has worked to identify war criminals and those charged with human-rights violations, ICE spokeswoman Virginia Kice told the Review-Journal.

The United States is seen as a “safe haven” for refugees and asylum seekers, ICE said, and war criminals and human-rights violators sometimes make it through the cracks to enter the country, as well.

“These aren’t war criminals,” Brelje, who also represents a dozen Phoenix-area men facing deportation, told the Times.

While some of his Phoenix clients were stationed with Serb forces in towns not far from Srebrenica, they were “grunts in the trenches” securing perimeter positions, not executing Muslims.